(1) Field of the Invention
This invention relates to hydrolyzable silanes which on hydrolysis generate byproducts having low vapor pressure (LVP) and to resinous compositions, e.g., organic resin-containing adhesives, sealants and coatings, incorporating such silanes.
(2) Description of Related Art
Conventional hydrolyzable organofunctional silanes are known for use as adhesion promoters, crosslinkers, surface modifiers and moisture scavengers (desiccants) in adhesive, sealant and coating compositions. These silanes are characterized by possessing one or more hydrolyzable methoxy or ethoxy groups that, in the presence of moisture, undergo hydrolysis and subsequent condensation to form stable silicon-oxygen-silicon or silicon-oxygen-metal bonds. Hydrolysis of these conventional hydrolyzable organofunctional silanes generates high vapor pressure byproducts such as methanol or ethanol. These volatile byproducts are undesirable for many types of consumer products due to concerns about exposing consumers to volatile organic compounds (VOCs). VOC emissions from consumer products have been, and continue to be, the subject of governmental regulation such as the State of California Air Resources Board's Regulation for Reducing Volatile Organic Compound Emissions from Consumer Products, Final Regulation Order, Subchapter 8.5, Consumer Products.
Following the manufacture of moisture curable resins, it is highly desirable that the resins be shielded from moisture so as to minimize any hydrolysis that might negatively affect the usefulness of products containing them Moisture curable resins if exposed to even small amounts of moisture at any time following their production and before the use of products containing them will experience some degree of premature curing ranging from negligible to excessive. The need to avoid a deleterious degree of premature curing of such resins can be readily appreciated, e.g., in the case of a moisture curable sealant which is packaged in a moisture-resistant cylindrical container. The sealant is discharged from the cylindrical container onto a substrate when and as desired by application of moderate force exerted by a hand-actuated piston. Exposure of the sealant to even small amounts of moisture while still in its container, e.g., the amounts of moisture that may be present in the sealant at the time of its packaging, initiates cure, resulting in an increase in the viscosity of the sealant and requiring an unduly high degree of force for its discharge from the container. This build-up of product viscosity over time, viewed as a storage stability problem, if not anticipated and suitably addressed can be a major drawback to the convenient and successful application of these products.
It has therefore been a practice to include a moisture scavenger in a moisture curable sealant, coating, adhesive or silane-containing resin component thereof in order to reduce the possibility or extent of such in-storage hydrolysis and subsequent condensation of the silane thereby conserving or increasing its storage stability. Among the moisture scavengers known in the art are vinyltrimethoxysilane and methyltrimethoxysilane. These compounds preferentially react with moisture thereby reducing the opportunity for excessive premature curing of the silane-containing organic resin component of the composition. However, upon application of the silane resin-containing composition, a conventional moisture scavenging vinyltrimethoxysilane or methyltrimethoxysilane component will also undergo hydrolysis and condensation producing significant amounts of volatile organic compounds (VOCs), specifically, monoalcohols such as methanol, an environmental safety hazard which continues to be the target of corrective legislation and administrative rule making.
Another common practice in the manufacture of coatings, adhesives and sealants is to incorporate into their formulations an adhesion-enhancing amount of a typically low molecular weight silane such as an aminosilane, ureido silane or epoxysilane. These hydrolyzable organofunctional silanes form bonds with the organic resin and the substrate onto which they are applied. As in the case of moisture scavenging vinyltrimethoxysilanes, adhesion-promoting silanes will also emit significant amounts of VOCs such as methanol and ethanol when undergoing hydrolysis which occurs upon application of compositions containing these hydrolyzable organofunctional silanes to the substrate.